Octopuses are the only smart invertebrate animals. Their brains are quite different from that of vertebrates like us:
Rather than being centralised and profoundly integrated, the octopus nervous system is distributed into components with considerable functional autonomy from each other. Of particular note is the arm nervous system: when severed, octopus arms still exhibit behaviours that are nearly identical to those exhibited when the animal is intact.
Achieving coherence of mind and purpose may come with tradeoffs. This makes it even more remarkable that a high level of coherence like that of an octopus can be achieved with a decentralized nervous system:
We need to go beyond vertebrate-based assumptions about phenomenal experience. Among these assumptions are the notions that consciousness is by necessity unified, that there is only one conscious field per organism, and that only the CNS can generate conscious fields. There is no better case study in these possibilities than octopus arms and their idiosyncratic capacities.
Nehaveigur 